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How to Cache Parsed JSON for Offline usage

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走了就别回头了
走了就别回头了 2020-12-30 15:06

I have parsed JSON successfully but now i want to Cache it for offline usage, even internet is not available, and if any new entry comes i want to cache that as well.

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2条回答
  • 独厮守ぢ
    独厮守ぢ (楼主)
    2020-12-30 16:05

    Why not just save it to cache folder of your app using something like this:

    String path = Environment.getExternalStorageDirectory() + File.separator + "cache" + File.separator;
File dir = new File(path);
if (!dir.exists()) {
    dir.mkdirs();
}
path += "data";
File data = new File(path);
if (!data.createNewFile()) {
    data.delete();
    data.createNewFile();
}
ObjectOutputStream objectOutputStream = new ObjectOutputStream(new FileOutputStream(data));
objectOutputStream.writeObject(actorsList);
objectOutputStream.close();

    And after, you can read it in any time using:

    List list = null;
File data = new File(path);
try {
    if(data.exists()) {
        ObjectInputStream objectInputStream = new ObjectInputStream(new FileInputStream(data));
        list = (List) objectInputStream.readObject();
        objectInputStream.close();
    }
} catch (IOException e) {
    e.printStackTrace();
} catch (ClassNotFoundException e) {
    e.printStackTrace();
}



    UPDATE: Okay, make class named ObjectToFileUtil, paste this code to created class
    


    package ;

import android.os.Environment;

import java.io.*;

public class ObjectToFileUtil {

    public static String objectToFile(Object object) throws IOException {
        String path = Environment.getExternalStorageDirectory() + File.separator + "cache" + File.separator;
        File dir = new File(path);
        if (!dir.exists()) {
            dir.mkdirs();
        }
        path += "data";
        File data = new File(path);
        if (!data.createNewFile()) {
            data.delete();
            data.createNewFile();
        }
        ObjectOutputStream objectOutputStream = new ObjectOutputStream(new FileOutputStream(data));
        objectOutputStream.writeObject(object);
        objectOutputStream.close();
        return path;
    }

    public static Object objectFromFile(String path) throws IOException, ClassNotFoundException {
        Object object = null;
        File data = new File(path);
        if(data.exists()) {
            ObjectInputStream objectInputStream = new ObjectInputStream(new FileInputStream(data));
            object = objectInputStream.readObject();
            objectInputStream.close();
        }
        return object;
    }
}

    


    Change < yourpackagehere > to your package name and don't forget to add  WRITE_EXTERNAL_STORAGE permission to AndroidManifest.xml. In your MainActivity add field
    


    private String dataPath;

    


    and replace your onPostExecute method of JSONAsyncTask class to 
    


    protected void onPostExecute(Boolean result) {
    dialog.cancel();
    adapter.notifyDataSetChanged();
    if(result) {
        try {
            dataPath = objectToFile(arrayList);
        } catch (IOException e) {
            e.printStackTrace();
        }
    } else {
        Toast.makeText(getApplicationContext(), "Unable to fetch data from server", Toast.LENGTH_LONG).show();
    }
}

    


    Now you can access get actorsList from File anytime when you want, by using
    


    try {
    actorsList = (ArrayList)objectFromFile(dataPath);
} catch (IOException e) {
    e.printStackTrace();
} catch (ClassNotFoundException e) {
    e.printStackTrace();
}

    


    If you want to save path of file after closing application you must save dataPath string (and load on application start), for example, using SharedPreferences.
    
    
    
             
    
                                                        
    
            
            
    
              
                
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